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IC 9117 



Bureau of Mines Information Circular/1986 



Transformer Fluid Fires 
in a Ventilated Tunnel 

By Margaret R. Egan 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 9117 

Transformer Fluid Fires 
in a Ventilated Tunnel 

By Margaret R. Egan 




UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



.at 




Library of Congress Cataloging in Publication Data: 



Egan, Margaret R 

Transformer fluid fires in a ventilated tunnel. 

(Information circular ; 9117) 

Bibliography. 

Supt. of Docs, no.: I 28.27: 9117. 

1. Mine fires. 2. Mine ventilation. 3. Electric transformers. I. Title. II. Series: Information 
circular (United States. Bureau of Mines) ; 9117. 



TN295.U4 



[TN315] 



622 s 



[622'.8] 



86-600288 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Instrumentation 2 

Fire tunnel 2 

Thermocouples 2 

Flow probes and pressure transducers 2 

Gas monitors 3 

Smoke monitors 3 

Fuel-consumption monitor 4 

Typical test procedure 4 

Calculations 4 

Product generation rates 4 

Combustion yields 4 

Heat-release rates 5 

Production constants 5 

Smoke particle diameters 5 

Burning rate 6 

Brand comparison results. 6 

Gas concentrations and heat production 6 

Smoke characteristics 8 

Combustion yields 8 

Production constants 8 

Discussion of results 8 

Conclusions 10 

Fuel comparison results and discussion 10 

Scaling results and discussion 11 

Appendix. — List of symbols 13 

ILLUSTRATIONS 

1. Schematic of intermediate-scale tunnel 3 

2. CO concentrations (A), CO2 concentrations (B), heat-release rates (C)» and 

heats of combustion (D) for three brands of transformer fluid 7 

3. Particle mass concentrations (A), number concentrations (5), and mass mean 
diameters (C) for three brands of transformer fluid 9 

4. Burning rates for gasoline and transformer fluid 12 

TABLES 

1. Average gas concentrations, heat-release rates, and heats of combustion for 

transformer fluid 7 

2. Toxic-gas concentrations for transformer fluid 8 

3. Smoke characteristics for transformer fluid 8 

4. Mean particle sizes and obscuration rates for transformer fluid 8 

5. Combustion yields for transformer fluid 8 

6. Production constants for transformer fluid 9 

7. Gas, heat, and smoke concentrations for the three fuels tested 10 

8. Normalized gas and smoke concentrations for the three fuels tested 10 

9. Particle size and obscuration rates for the three fuels tested 11 

10. Production constants for the three fuels tested 11 





UNIT OF MEASURE ABBREVIATIONS USED IN 


THIS REPORT 


cm 


centimeter 


mg/m 3 


milligram per cubic meter 


cm/min 


centimeter per minute 


pg/m 3 


microgram per cubic meter 


°F 


degree Fahrenheit 


min 


minute 


g 


gram 


ym 


micrometer 


g/cm 3 


gram per cubic centimeter 


m 3 /s 


cubic meter per second 


g/(m 3, ppm) 


gram per (cubic meter 
times part per million) 


P 


particle 






p/cm 3 


particle per cubic i 


g/g 


gram per gram 




centimeter 


g/kJ 


gram per kilo joule 


pet 


percent 


g/s 


gram per second 


p/g 


particle per gram 


kg 


kilogram 


p/kJ 


particle per kilojoule 


kJ/g 


kilo joule per gram 


ppm 


part per million 


kW 


kilowatt 


ppm/min 


part per million 
per minute 


In 


logarithm, natural 










psi 


pound per square inch 


m 


meter 







TRANSFORMER FLUID FIRES IN A VENTILATED TUNNEL 

By Margaret R. Egan 1 




ABSTRACT 

The Bureau of Mines subjected three commercially available brands of 
transformer fluid to a series of combustion studies. The experiments 
were conducted in the intermediate-scale fire tunnel, which was designed 
to simulate environmental conditions in underground mines. The work was 
divided into three phases. In phase one, the brands were compared for 
gas production, smoke characteristics, and combustion yields. In phase 
two, the production constants of transformer fluids and other fuels were 
compared for the rate of formation of gas and smoke as a function of 
fire size. In phase three, several diameters of liquid-pool fires were 
compared in terms of fire size and burning rate. 

These transformer fluid measurements will be added to the existing 
coal and wood data that can be used as a basis of comparison for future 
studies of other mine combustibles. Further research into the combus- 
tion product emissions from combustible materials found in underground 
mines will lead to improved and realistic fire detection and suppression 
systems. 

'Chemist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 



INTRODUCTION 



The Bureau of Mines conducts research 
to ensure that mines are safe and health- 
ful places to work. Exceptional circum- 
stances, such as an underground fire, 
pose additional problems involving health 
and safety. Among these dangers are 
those affecting escape and rescue. Early 
fire detection increases the opportunity 
for human escape. Rescue efforts are 
often hampered by reduced visibility due 
to smoke and the potential toxicity of 
the combustion products. More efficient 
detection devices and rescue equipment 
can be designed once the hazardous pro- 
ducts of combustible materials are known. 
Therefore, the smoke characteristics of 
fires in ventilated mine passageways are 
investigated by the Bureau. 

These experiments are part of a series 
of continuing projects in which combus- 
tible materials are burned in a simulated 



mine environment. Previous studies^ have 
shown that the intermediate-scale fire 
tunnel used for the current studies can 
successfully predict full-scale fire 
conditions. 

Transformers are used to produce elec- 
trical power needed to operate mine mach- 
inery. Heat, which is an inherent by- 
product of this process, is removed by 
transformer fluid. Fires are potential 
risks whenever petroleum oil, the basic 
component of transformer fluid, is used 
in any electrical equipment. 

The objectives of this study are (1) to 
compare three brands of transformer fluid 
for gas production and smoke characteris- 
tics, (2) to compare these evaluations 
with similar data for wood and coal, and 
(3) to compare fire sizes and burn- 
ing rates of several pool sizes of 
transformer fluid. 



INSTRUMENTATION 



FIRE TUNNEL 



THERMOCOUPLES 



The transformer fluid fires were con- 
ducted in an intermediate-scale fire tun- 
nel located at the Bureau's Pittsburgh 
Research Center. A diagram of the tunnel 
with its data-acquisition system is shown 
in figure 1. The tunnel measures 0.8 m 
wide by 0.8 m high by 10 m long and is 
divided into three sections. The first 
horizontal section begins at the air- 
intake cone, which gradually enlarges to 
a hinged portion that can be lifted to 
allow entrance for the placement of oil 
pan. Next is the fire zone in which is 
located the gas burner followed by the 
oil pan. The fire zone and the remaining 
horizontal section are lined with fire- 
brick and instrumented with thermo- 
couples, flow probes, and sampling ports. 
The diffusing grid begins the vertical 
section of the tunnel. Located in this 
section is an orifice plate that can be 
manually adjusted to attain the desired 
airflow. The final section is horizontal 
and ends at an exterior exhaust fan. 



The thermocouple arrays were located 
1.57, 2.36, 3.15, 4.72, 6.30, and 7.87 m 
from the gas burner. Additional thermo- 
couples are located on the air-intake 
cone and at the exhaust. In all, a total 
of 28 thermocouples were used to measure 
the temperature distributions resulting 
from the fires. Their locations are 
shown in figure 1 . 

FLOW PROBES AND PRESSURE TRANSDUCERS 

The air pressure produced by the ex- 
haust ventilation is detected by the 
transducer. As pressure increases, the 
capacitance decreases. This change is 
then converted to a linear electric sig- 
nal. Nonlinearily is described as <±0.1 

2 Lee, C. K. , R. F. Chaiken, J. M. Sin- 
ger, and M. E. Harris. Behavior of Wood 
Fires in Model Tunnels Under Forced 
Ventilation Flow. BuMines RI 8450, 1980, 
58 pp. 



INTERMEDIATE-SCALE FIRE TUNNEL 
10- m length 



I2 _ m length 
0.6l _ m diam duct 



1.22 m 



0.8 -m square duct 



Fire zone 



intake 




_*-?_B_ 



u Load cell 




Air 



Manually 
adjustable 
orifice plate 



7 exhaust 
Ventilation 

fan 
( 2-speed ) 



1 — Diffusing grid 



-Q305 - rTrdiam 
entrance duct 
( hinged and movable) 



CALOUT/DECNET- 



Tapered-element 

oscillating 

microbalance 



Condensation 
nuclei monitor 



CO meter 



CO2 meter 



Pressure transducers 



MM 



48" 
channel 

data- 
acqui 
sition 
system 



3X 
= detector 



t...28— ' 
thermocouples 



i_ -Load cell 

- Digital input 

for CNM 

range 



PDP 
I /44 



Control 
terminal 



VAX 
11/780 



Printer 



VAX 
terminal 



CALCOMP 
plotter 



KEY 

Pressure transducer (flow probe) • Thermocouples 

Differential pressure transducer ■ Sampling ports 

3X detector 

FIGURE 1.— Intermediate-scale fire tunnel (top) and data-acquisition system (bottom). 



pet full range of the output or ±0.00001 
psi differential. The locations of the 
pressure transducers are also shown in 
figure 1. 



GAS MONITORS 

The carbon monoxide (CO) 
sures accurately within 1 
range or ±5 ppm. 

The carbon dioxide (C0 2 ) 
sures accurately within 1 
range or ±250 ppm. 

SMOKE MONITORS 



The number concentration (N Q ) was 
obtained with a condensation nuclei 



analyzer mea- 
pct of full 

analyzer mea- 
pct of full 



monitor, manufactured by Environment One 
Corp. ^ The monitor measures the con- 
centration of submicrometer airborne par- 
ticles (p) using a cloud chamber. The 
particulate cloud attenuates a light beam 
that ultimately produces a measurable 
electrical signal. The accuracy is 
stated as ±20 pet of a point above 30 pet 
of scale on the linear ranges, 3,000 to 
3000,000 p/cm3. 

The mass concentration (M Q ) was ob- 
tained by a TEOM tapered-element os- 
cillating microbalance, developed by 
Rupprecht & Patashnick Co. , Inc. It 

^Reference to specific equipment does 
not imply endorsement by the Bureau of 
Mines. 



measures the mass directly by depositing 
the particles on a filter attached to an 
oscillating tapered element. The change 
in the oscillating frequency of the tap- 
ered element is directly proportional to 
the change in mass. The apparatus is 
capable of measuring dust concentrations 
with a better than 10-pct accuracy at the 
250-ug/m 3 level. 

A three-wavelength light transmission 
technique was also used to measure smoke 
characteristics and obscuration. White 
light was transmitted through a smoke 
cloud to the detector. The beam was 
split into three parts, and each passed 



through an interference filter centered 
at wavelengths of 0.45, 0.63, or 1.00 pm. 
Each photodiode output was amplified and 
recorded as a linear electric signal. 
This technique was developed by Bureau 
personnel. 4 

FUEL-CONSUMPTION MONITOR 

The weight-loss data were obtained by a 
strain-gauge conditioner in conjunction 
with a load cell, which has a range up to 
22.68 kg. The accuracy of the strain 
gauge is stated as 0.05 pet of full scale 
or ±11.3 g. 



TYPICAL TEST PROCEDURE 



The transformer fluid was poured into a 
stainless steel pan inside the tunnel. 
The shaft of the pan extended through the 
tunnel floor and was supported on the 
load cell so that continuous weight loss 
could be recorded. 

Prior to each experiment, background 
readings were obtained after the cone was 
closed and the exhaust fan was started. 
All instruments were continuously scanned 
and recorded throughout the experiment. 

A gas jet, located immediately upstream 
from the pan, was the igition source. 
The burner flow rate was adjusted so 
that the flame licked the side of the 



oil-filled pan. The flash point of the 
transformer fluid, as stated by the man- 
ufacturers, is about 300° F. At a ven- 
tilation rate of approximately 0.65 m 3 /s, 
the transformer fluid took about 1 min to 
ignite. The ventilation rate was then 
lowered to approximately 0.47 m 3 /s during 
the steady-state burning. 

The gas burner was turned off once 
the transformer fluid had ignited. The 
flames spread quickly, engulfing the en- 
tire pan within 1 min. The flames began 
to die down as the transformer fluid was 
consumed. The experiment was concluded 
when the flames were no longer visible. 



CALCULATIONS 



It is necessary to measure certain pa- 
rameters in order to compare the steady- 
state combustion products and utilmately 
the hazards of various fuels. Among 
these values are gas concentrations, mass 
and number concentrations of smoke par- 
ticles, ventilation rate, and mass-loss 
rate. Other combustion properties can be 
calculated once these are known. 

PRODUCT GENERATION RATES 

In a ventilated system, the generation 
rates (Gx)'of CO2 and CO are related to 
the bulk average concentration increase 
above ambient, ACO2 and ACO, by the 
expressions 



and 



Geo = M C0 V A ACO, (2) 



Geo, = M C0 , V A AC0 2 



(1) 



where Mco 2 = l- 97 x 10_3 g/(m 3 *ppni) ; 

M C o = 1.25 x 10 -3 g/m 3 «ppm); 

and V A = incoming cold gas flow, 
m 3 /s. 



COMBUSTION YIELDS 

Once the generated rates are known and 
the mass-loss rate of the fuel (Mf) is 

4 Cashdollar, K. L., C. K. Lee, and 
J. M. Singer. Three-Wavelength Light 
Transmission Technique To Measure Smoke 
Particle Size and Concentration. Appl. 
Opt., v. 18, No. 11, 1979, pp. 1763-1769. 



calculated using the load-cell assembly, 
the true yield of the combustion product 
(Yx) can be calculated by the expression 



Y X = Gx/Mf. 



(3) 



The yields for mass (M ) and number 
(N ) concentrations are calculated in a 
similar manner by the expression 



Yx = 



AX C X V A 

• ! 

Mf 



(4) 



where 



Cx = appropriate units conversion factor: 
1.00 x 10" 3 when M Q is in mg/m 3 or 
1.00 x 10 6 when N is in p/cm 3 ; 

and 

AX = smoke concentration increase above 
ambient (when M is measured as mg/ 
in 3 and N is measured as p/cra 3 ). 

HEAT-RELEASE RATES 

It has been shown^ that the actual 
heat-release rate realized during a fire 
can be calculated from the expression 



Qa = 



He 
Kco. 



Geo. 



He - Heo (Keo) 
Kco 



Geo. 



(5) 



where Qa = actual heat release, kW; 



He = net heat of complete combus- 
tion of the fuel (40.7 kj/g 
for transformer fluid); 



Substituting the values in equations 1, 
2, and 5 yields 

Qa = V A [0.0251 (AC0 2 ) 

+ 7.07 x 10~ 3 (ACO)]. (6) 

Since measurements of V A , ACO2, and 
ACO were made continuously, the actual 
heat-release rates could be calculated 
using equation 6. 

A typical fire rarely realizes the 
state of complete combustion. For this 
reason, the actual heat of combustion 
(Ha) during a fire is usually less than 
the total heat of combustion (He). By 
measuring both the actual heat-release 
rate, equation 6 above, and the fuel 
mass-loss rate (Mf), the actual heat of 
combustion can be calculated from the 
expression 



H A = QA/Mf. 



PRODUCTION CONSTANTS 



(7) 



In an actual mine fire, it is often 
difficult, if not impossible, to calcu- 
late the actual heat of combustion. 
Moreover, since the true yield of a com- 
bustion product depends upon this infor- 
mation, significant errors can result in 
predicting the resultant concentration 
increases. For flaming fires, the rel- 
ative hazards tend to increase with the 
actual heat-release rate that results. 

For this reason, production constants 
or beta values (Bx) can be calculated for 
a given product by the expression 



3x = Gx/Qa« 



(8) 



Kco 2 = stoichiometric yield of CO2 
= 3.19 g/g; 



Heo = heat of combustion of CO 
=10.1 kJ/g; 

and Kco = stoichiometric yield of CO 
= 2.58 g/g. 

5 Tewarson, A. Heat Release Rate in 
Fires. Fire and Mater., v. 4, No. 4, 
1980, pp. 185-191. 



Using the rate of formation of gas or 
smoke as a function of the fire size 
is also beneficial in comparing the 
combustion hazards of different fuels. 

SMOKE PARTICLE DIAMETERS 

Measurements of both number and mass 
concentrations of the smoke provide 
important information relative to the 
yields, equation 4, and production con- 
stants, equation 7. They can also be 



used to calculate the average size of the 
smoke particles, with the expression 



In T (XI. 00) In T (XI. 00) 



TTd m 3 



p p N = 1 x 10 3 M , (9) 



where p p = individual particle den- 
sity, g/cm 3 ; 



particle, ym; 

and 1 x 10 3 = the appropriate units con- 
version factor. 

Assuming a value of p p = 1.4 g/cm 3 , 
then the mass mean diameter of the 
particles can be calculated from 



d m = 11 



■" Ct) 



1/3 



(10) 



where the particle diameter is expressed 
in micrometers. 

Using the three-wavelength smoke detec- 
tor, the transmittance (T) of the light 
through the smoke can be calculated for 
each wavelength. The extinction-coeffi- 
cient ratio can be calculated for each 
pair of wavelengths by the following log- 
transmission ratios: 



or 



In T (X0.63) In T (X0.45) 

In T (X0.63) . 
In T (X0.45) 



(11) 



Using these extinction coefficients and 
the curve found by Cashdollar, *> the mean 
particle size (d 32 ) can be determined. 

The smoke-obscuration rate is the per- 
centage of the ratio of the light de- 
tected after passing through the smoke 
compared with the background light. 

BURNING RATE 

It is difficult to compare the hazards 
from liquid-fuel fires with those of 
fires involving solid fuels such as coal 
and wood. The major reason for this dif- 
ficulty is the speed with which liquid- 
fuel fires develop compared with that for 
solid-fuel fires. However, liquid-pool 
fires can be compared by using the total 
burning rate, which is calculated by di- 
viding the depth of the fuel (in centi- 
meters) by the burning time (in minutes). 
This information can then be used to 
compare various pan diameters. 



BRAND COMPARISON RESULTS 



All the values listed in this report 
are an average of steady-state burning 
stage that was arbitrarily selected to be 
the 20th to the 30th minute after igni- 
tion. Ten experiments were completed us- 
ing three brands of transformer fluid: 
four with Texaco 7 fluid and three each 
with Shell and Gulf fluids. All three 
brands showed similar results for gas 
production, heat release, and heat of 
combustion. However, the tested brands 
showed somewhat different results for 
smoke characteristics. 

GAS CONCENTRATIONS AND HEAT PRODUCTION 

The CO and CO2 concentrations, heat- 
release rates, and heats of combustion 

6 Figure 9 of work cited in footnote 4. 



graphs for an average test of each brand 
of transformer fluid are found in figure 
2. The initial spike found on the CO2, 
heat-release rate, and heat of combustion 
was caused by the natural gas burner. 

The CO and CO2 productions were contin- 
uously monitored throughout the experi- 
ment. The CO concentration remained 
fairly constant, rising slightly as the 
flames died. The CO 2 concentration grad- 
ually rose at an average rate of 22 ppm/ 
min as the fuel was consumed. 

The heat-release rate remained fairly 
constant for most of the experiments, in- 
creasing slightly just before the flames 
died. The average mass loss was 2.026 g, 
at a rate of 0.866 g/s . The heat of 

'Reference to specific brands does not 
imply endorsement by the Bureau of Mines. 






i 


i i 


1 

B 


" 






K\ 


ll 




r / 


\\ 



I 


ti 


^-jpjfcr^ 


1 rp 






\\ 


"1 \M 






\\ 


"I 






l\ - 


1 






1\ . 

1 


- 






1 


- 






\ - 






I 1 






FIGURE 2.— CO concentrations (A), C0 2 concentrations (S), heat-release rates (C), and heats of combustion (0) 
for three brands of transformer fluid. 



combustion also remained fairly constant 
throughout the steady-state burning but 
rose sharply just before the fuel was 
completely consumed. The average values 
for each brand and the grand average 
(which includes all experiments) are 
listed in table 1. 

During a 30-min period after igni- 
tion, six gas samples were taken, each 5 
min apart. All brands showed a slight 
decrease in oxygen and a slight increase 



TABLE 1. - Average gas concentrations, 
heat-release rates, and heats of 
combustion for transformer fluid 



Brand 


CO, 
ppm 


C0 2 , 
ppm 


Qa» 

kW 


kJ/g 




120 

97 

120 


1,682 
1,871 
1,784 


20.3 
22.2 
21.0 


22.9 




25.3 

24.5 




113 


1,769 


21.1 


24.1 



in argon and nitrogen concentrations. 
These samples were also tested for hydro- 
carbons C1-C3. The brands showed very 
little variation. The concentrations in- 
creased slightly as combustion proce- 
eded. Table 2 lists the averages for 
each brand. 

SMOKE CHARACTERISTICS 

The number concentration slowly in- 
creased until the fuel was almost 
completely consumed, then it started to 
drop. The mass concentration varied 
throughout the experiments. An average 
was taken during the steady-state burning 
when it was the most stable. Using these 
values, the mass mean diameter was 
calculated. The average values for each 
brand are listed in table 3. The mass 
number concentrations and the mass mean 
diameters for an average test of each 
brand are found in figure 3. 

Using the three-wavelength smoke de- 
tector, the average mean particle size 
(d32) was calculated for each wavelength. 
These averages and the obscuration rates 
for each brand are listed in table 4. 

COMBUSTION YIELDS 

The gas concentration yields, as ex- 
pected, showed little variation. How- 
ever, the mass and number concentration 
yields of smoke particles showed a wide 
variation between brands. The average 
yields are listed in table 5. 



PRODUCTION CONSTANTS 

The production constants or beta values 
were calculated as a function of the fire 
size. For the tested brands of trans- 
former fluid, the fire sizes were very 
similar. Therefore, it is expected that 
the beta values reflect the same vari- 
ability as the gas and smoke concen- 
trations. Table 6 lists the average pro- 
duction constants for each brand. 

DISCUSSION OF RESULTS 

The Shell transformer fluid generated a 
slightly larger CO2 concentration, thus 
increasing the corresponding fire size 

TABLE 2. - Toxic-gas concentrations 
for transformer fluid, ppm 



Brand 


Methane 


Ethane 


Ethy- 
lene 


Acety- 
lene 


Texaco. . . 
Shell.... 
Gulf 


22.1 
15.3 
22.5 


4.5 

1.7 

.9 


19.0 
11.5 
16.9 


9.8 
16.6 
16.2 



TABLE 3. - Smoke characteristics for 
transformer fluid 



Brand 



Texaco. . . . 

Shell 

Gulf 

Average, 



No, 
p/cm 3 



1,567,250 

1,126,900 

416,533 



1,089,930 



Mo, 
mg/m 3 



40.6 

9.0 

58.1 



35.3 



dm, 
ym 



0.309 
.223 
.601 



.386 



TABLE 4. - Mean particle sizes and obscuration rates for transformer fluid 



Brand 


In T (X0.63) 

In T (X0.45)' 

ym 


In T (XI. 00), 

In T (X0.45)' 

ym 


In T (XI. 00) 
In T (X0.63)' 

ym 


Average 

d 32, 
ym 


Obscuration 

rate, 

pet 




0.302 
.339 
.336 


0.351 
.395 
.431 


0.391 
.440 
.538 


0.348 
.391 
.435 


39.9 


Shell 


40.8 




59.6 




.323 


.388 


.450 


.387 


46.1 



TABLE 5. - Combustion yields for transformer fluid 



Brand 


Yco, 
g/g 


V C0 2 , 
g/g 


10^°p/g 


g/g 


Brand 


Yco, 
g/g 


Yco 2 » 
g/g 


Yn , 
10H°p/g 


g/g 




0.083 
.064 


1.829 
1.952 


8.85 
5.92 


0.021 
.005 


Average. . 


0.081 


1.894 


2.23 


0.031 




.077 


1.885 


5.99 


.019 




2.0 


I 1 I i ■ 
A A S 


1.8 


l\l\ 


1.6 


A j \ 


» 1.4 


1 VI \ A 


E 


i \ / \ 


o 10 

z 
o 




o 

cc 0.8 


-ikf / v v \ 


UJ 
CD 


W'-ajV J \ 


§ 0.6 

z 

0.4 






s. 


0.2 


"S - 




V 

1 1 1 1 



10 20 30 40 50 

TIME, min 



FIGURE 3.— Particle mass concentrations (A), number 
concentrations (B), and mass mean diameters (C) for 
three brands of transformer fluid. 



TABLE 6. - Production constants for transformer fluid 



Brand 


Bco> 
10~ 3 g/kJ 


Bco ? » 
10~ 2 g/kJ 


&N rt > 

10 10 p/kj 


lO" 1 * g/kJ 




3.47 
2.53 
3.30 


7.69 
7.74 
7.70 


3.77 

2.34 

.91 


9.17 




1.95 
12.60 




3.14 


7.71 


2.48 


7.75 



(Q/\) and the heat of combustion (Ha). It 
also produced less CO, methane, and ethy- 
lene. However, the Texaco fluid pro- 
duced more ethane but less acetylene than 



the other tested brands. These analyses 
were based on relatively few experiments 
and may only reflect the range of gas 
production. Considering this, the gas 



10 



concentrations generated by the tested 
brands of transformer fluid were similar. 

The differences between the brands were 
more evident in their smoke character- 
istics. The most noticeable variations 
were the Shell fluid's 55 pet lower mass 
concentration and the Gulf fluid's 82 pet 
lower number concentration. These low 
values were also reflected in the re- 
duced combustion yields and production 
constants. 

Since the particle size can be calcu- 
lated by two independent methods, the di- 
ameters obtained by one method should 
confirm those obtained by the other. The 
calculations indicate good agreement be- 
tween the average d m and d 32 . 

However, differences were apparent in 
comparing the particle sizes of each 
brand. The small mass concentration of 
the Shell fluid has lowered the d m , while 



the d 32 approximates the average. The 
low number and high mass concentrations 
for the Gulf fluid resulted in the 
largest calculated d m . By either method, 
the Gulf fluid produced the largest par- 
ticles. This was corroborated by its 
high obscuration rate. 

CONCLUSIONS 

The results of these experiments showed 
little variation between the transformer 
fluid brands for CO and CO production, 
heat release, and heat of combustion. 
However, the smoke-characteristic calcu- 
lations indicate that the Gulf fluid 
produced the heaviest and thickest 
smoke, while the Shell fluid gen- 
erally produced the lowest toxic-gas 
concentrations . 



FUEL COMPARISON RESULTS AND DISCUSSION 



Earlier wood and coal experiments were 
conducted in the same intermediate-scale 
fire tunnel. Since the same instrumenta- 
tion was used in the collection of 
all the data, it was possible to com- 
pare them. The gas, heat, and smoke 
concentrations for the three fuels stud- 
ied are found in table 7. 



In these experiments, wood produced the 
most heat relative to the fuel consumed. 
For better comparison, the other fuels 
were normalized to this fire intensity. 
Table 8 has these normalized values. 
Burning coal produced the most hazardous 
smoke and gas concentrations. 



TABLE 7. - Gas, heat, and smoke concentrations for 
the three fuels tested 



Fuel 


CO, 
ppm 


co 2 , 

ppm 


kW 


No. 
10 6 p/cm 3 


mg/m 3 




145 

76 

113 


6,759 

909 

1,769 


110.2 

5.4 

21.1 


6.04 
1.68 
1.09 


49.1 




7.7 




35.3 



TABLE 8. - Normalized gas and smoke concentrations for 
the three fuels tested 



Fuel 



CO, 
PPm 



C0 2 , 
PPm 



N , 
10 6 p/cm 3 



mg/m 3 



Wood 

Coal 

Transformer fluid. 



145 

1,551 

590 



6,759 

18,550 

9,239 



6.04 

34.28 

5.69 



49.1 
157.1 
184.4 



11 



TABLE 9. - Particle size and obscuration rates for 
the three fuels tested 



Fuel 



d m » 


d32» 


Obs 


>curation rate, 


ym 


urn 




pet 


0.223 


ND 




8.6 


.177 


0.272 




18.2 


.386 


.387 




46.1 



Wood 

Coal 

Transformer fluid. . 
ND Not determined. 



TABLE 10. - Production constants for the three fuels tested 



Fuel 



Wood , 

Coal 

Transformer fluid. 



6co> 
10- 3 g/kj 



1.58 
5.26 
3.14 



Bco 2 > 
10~ 2 g/kj 



10.44 
8.89 
7.71 



10 10 p/kj 



5.79 

11.29 

2.48 



1Q- 1 * g/kj 



4.93 
4.08 
7.75 



Transformer fluid produced a thick, 
dense smoke. It surpassed coal in the 
mass of smoke particles. It also pro- 
duced the largest particle size and ob- 
scuration rate. The values can be 
found in table 9. 

Note the discrepancy between the d m and 
the d32 for coal. The d32 may be less 
reliable because it is determined by the 
complex refractive index of the par- 
ticles, which is not precisely known. If 
the refractive index used in the calcu- 
lations is incorrect, then the diameter 
will be inaccurate. However, the obscur- 
ation rates do indicate that the particle 
diameter for coal should be smaller than 
that calculated for transformer fluid. 



Coal generated the most CO and smoke 
particles, using the formation rate of 
gas and smoke as a function of the heat 
produced. Transformer fluid produced the 
largest mass concentration. These values 
are confirmed by the normalized concen- 
trations found in table 8 in which wood 
was found to generate the most CO 2 rela- 
tive to the fire size. The production 
constants are found in table 10. 

Based on these experiments, coal was 
the most hazardous of the fuels studied. 
However, transformer fluid produced 
the thickest smoke with the largest 
particles. 



SCALING RESULTS AND DISCUSSION 



In liquid-fuel fires, the surface area 
of the pool determines the intensity of 
the fire. In order to study this phenom- 
enon, three round pans (25, 50, and 71 cm 
diam), filled with transformer fluid, 
were used. These experiments followed 
the same test procedure as described 
above. Texaco transformer fluid was used 
for all the scaling studies. 

Only one experiment was completed using 
the 71-cm pan because the flame intensity 
was so great that the range of most of 
the smoke and gas detectors was exceeded. 
A 50-cm pan was used in two experiments 
but, again, the instruments were reaching 



their upper limits. In order to repeat 
the experiments using the larger pans, 
the gas and smoke monitors would have to 
be disconnected. The remaining four ex- 
periments were the ones previously 
reported in the portion on comparison of 
brands. 

Gasoline scaling studies were reported 
by Hertzberg. 8 In those experiments, the 
burning time was plotted as a function 
of the pool diameter. In figure 4, the 

8 Hertzberg, M. The Theory of Free 
Ambient Fires. Combust. and Flame, v. 
21, 1973, p. 202. 



12 



0.5 



i 1 r 




i i i i i 



20 



30 40 50 60 
POOL DIAMETER, cm 



70 80 90 



FIGURE 4.— Burning rates for gasoline and transformer 
fluid. 



transformer fluid results were super- 
imposed on his figure 3C The two 
smaller pan sizes showed good agreement. 
But the 71-cm pan result was incon- 
sistent with the gasoline data. The 
size of the pan approximated the entry 
width of the tunnel, which could have 
limited the oxygen supply to the fire. 
This would have reduced the combustion 
rate, thus increasing the burning time. 
To test this theory, higher ventilation 
rates could be used to increase the 
available oxygen supply. Future scal- 
ing experiments should be conducted 
without the delicate gas and smoke 
instrumentation. 



C 244 ! 



13 



dm 

<*32 

Geo 

GC0 2 

Gx 

H A 

H C 

HCO 
Keu 
Kuu 2 
M co 

Mco, 



conversion factor of a combustion 
product 

mass mean diameter, ym 

mean particle size, ym 

generated rate of CO, g/s 

generated rate of CO2, g/s 

generated rate of a combustion 
product, g/s 

actual heat of combustion, kj/g 

net heat of combustion of the 
fuel, kJ/g 

heat of combustion of CO, kj/g 

stoichiometric yield of CO, g/g 

stoichiometric yield of CO2, g/g 

density of CO, g/(m 3 *ppm) 

density of CO2, g/(m 3 *ppm) 



APPENDIX.— LIST OF SYMBOLS 

Mf fuel mass loss rate, g/s 



M particle mass concentration, 
mg/ra 3 

N particle number concentration, 
p/cm 3 

Qa actual heat of combustion, kW 

T transmission of light, volts 

V A ventilation rate, m 3 /s 

Yx 



3x 

AX 

X 
Pp 



yield of a combustion product, 
g/g or p/g 

grams of product per unit kilo- 
joule of heat release 

measured change in a given 
quantity 

wavelength, ym 

individual particle density, 
g/cm 3 



A U.S. GOVERNMENT PRINTING OFFICE: 1986-605-017/40.100 



INT.-BU.0F MINES,PGH.,PA. 28377 



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Pittsburgh, Pa. 15236 



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